The present invention relates in general to chemical vapor deposition reactors, and more particularly, to metal organic chemical vapor phase deposition reactors. Still more particularly, the present invention relates to rotating wafer reactors in which one or more gasses are injected onto the surface of a rotating wafer carrier holding a wafer for growing various epitaxial layers and films thereon, and in particular, films of silicon carbide.
Metal organic chemical vapor deposition (MOCVD) reactors have taken various forms, including horizontal reactors in which the wafer is mounted at an angle to the impinging process gases; horizontal reactors with planetary rotation in which the gases pass across the wafers; barrel reactors; and recently, vertical high-speed rotating disk reactors in which the gas or gases are injected downwardly onto a substrate surface which is rotating within a reactor. These types of MOCVD reactors have been found useful for wide varieties of epitaxial compounds, including various combinations of semiconductor single films and multilayered structures such as lasers and LED""s.
Deposition of certain materials such as SiC semiconductor material requires wafer temperature levels up to about 1800xc2x0 C. in a hydrogen environment with temperature uniformity of about +/xe2x88x925xc2x0 C. during long deposition runs, e.g., up to 6-8 hours. Conventional radiant heating elements made of graphite cannot provide this temperature level especially in the hydrogen environment. Radiant heating elements made of tungsten cannot provide temperature stability due to dimensional non-stability, i.e., warpage. As a result, induction heating has been used when high temperature levels such as about 1500-1800xc2x0 C. have to be provided in a hydrogen environment.
Vertical high speed MOCVD rotating disk epitaxial reactor technology has been known to provide ideal flow and thermal conditions for SiC growth. Pancake type induction coils located below a susceptor in conventional reactors can provide uniform heating for the susceptor and wafer carrier. The wafer carrier has to be transferred from the load lock to the reactor (to prevent reactor explosion to atmosphere) and therefore located on the susceptor only under gravity force. One problem with this approach is levitation of the wafer carrier due to interaction between induction coil current and current generated in the wafer carrier. For example, as shown in FIG. 1, a known MOCVD reactor includes a susceptor 100 connected for rotation to a spindle 102. The susceptor 100 is positioned overlying a pancake type induction heating device 104 in the nature of a spiral coil. The induction heating device 104 is generally the type known in the art which is suitable for heating the reaction chamber to a temperature up to about 1800xc2x0 C. in a hydrogen environment as is required for the epitaxial deposition of SiC. A wafer carrier 106 supporting multiple wafers 108 is removably positioned on the top surface of the susceptor 100.
Dashed lines 110 schematically represent the induction magnetic field created by the induction heating device 104 to provide its heating. The wafer carrier 106 being carried by the susceptor 100 is positioned within the strong induction magnetic field created by the induction heating device 104. The wafer carrier 106 is accordingly heated mostly by the induction field and partially by heat radiation from the susceptor 100. It has been found that the strong magnetic field 110 generated by the induction heating device 104, particularly when heating wafers 104 to a temperature of about 1800xc2x0 C. as required for SiC epitaxial deposition, results in the magnetic field being sufficiently strong to cause levitation of the wafer carrier 106. The resulting levitation of the wafer carrier 106 causes its decoupling from the induction heating device 104 and susceptor 100 thereby making further heating or maintaining process temperature with the MOCVD reactor impossible.
Applicants have attempted various ways to eliminate wafer carrier levitation. For example, Applicants have increased wafer carrier (usually made of graphite with SiC coating) weight by increasing its thickness. This, however, has resulted in an undesirable temperature gradient across the thick wafer carrier and unavoidable cracking of the SiC layer. Another approach was to make the wafer carrier of Mo or W having a higher density than graphite. These materials although useful generally cannot be obtained with the same high purity as SiC coated graphite and will contaminate the deposition process. Another approach pursued by Applicants was the use of a locking mechanism between the wafer carrier and susceptor. As the locking mechanism is present in the reactor chamber at a very high temperature (high diffusion rates), it is subjected to the SiC deposition, as well as fusing together by diffusion under the long processes times generally used, e.g., 6-8 hours. As a result of the SiC coating, one cannot expect reliable performance from this locking system.
Accordingly, there is an unsolved need for designing a reactor for depositing, such as by chemical vapor deposition, a film of material, such as an epitaxial film of SiC, onto a wafer which prevents levitation of the wafer carrier as a result of the induction magnetic field generated by the induction heating device.
It is an object of the present invention to provide a reactor for depositing a film or material layer onto a wafer which is operative in a temperature range of up to about 1800xc2x0 C. for deposition of various materials such as epitaxial SiC.
Another object of the present invention is to provide an induction heated chemical vapor deposition reactor wherein the wafer carrier is significantly decoupled from the induction magnetic field created by the induction heating device.
Another object of the present invention is to provide an induction heated chemical vapor deposition reactor which enables efficient heating of the wafer carrier without the use of mechanical clamps for maintaining the wafer carrier in contact with the susceptor.
According to the present invention the susceptor has a thickness sufficient to significantly decouple the wafer carrier from the induction field created by the induction heating device eliminating the levitation effect. In this case, the wafer carrier is generally heated only by radiation from the susceptor that is heated by the induction coil. Required carrier/susceptor thickness ratio depends on their materials of construction, induction coil frequency, set up geometry and can be defined by modeling using Finite Element Analysis with following fine tuning by experimental iteration.
In accordance with one embodiment of the present invention there is described a reactor for depositing a film of material onto a wafer, the reactor comprising a reactor chamber, an induction heating device, a susceptor having a bottom surface facing the induction heating device and a top surface facing away from the induction heating device, the top surface operative for supporting a wafer carrier having at least one wafer for depositing a film of material thereon, wherein the susceptor is constructed whereby an induction magnetic force generated by the induction heating device at the top surface of the susceptor is insufficient to cause levitation of the water carrier from the susceptor.
In accordance with another embodiment of the present invention there is described a reactor for depositing an epitaxial film of SiC onto the surface of a wafer, the reactor comprising a reactor chamber, an induction heating device operative for heating the wafer to a temperature greater than about 1600xc2x0 C., a susceptor having a bottom surface facing the induction heating device and a top surface facing away from the induction heating device, and a wafer carrier positionable on the top surface of the susceptor for supporting at least one wafer for depositing an epitaxial film of material thereon within the reactor chamber, wherein the top surface of the susceptor is positioned at a location sufficiently remote from the induction heating device such that an induction magnetic force generated thereat by the induction heating device is insufficient to cause levitation of the wafer carrier therefrom.
In accordance with another embodiment of the present invention there is described a method for preventing levitation of a wafer carrier in a reactor for depositing an epitaxial film of material onto a wafer supported by the wafer carrier, the reactor including a susceptor having a surface for supporting the wafer carrier overlying an induction heating device, the method comprising constructing the susceptor whereby an induction magnetic force generated by the induction heating device at the surface of the susceptor is insufficient to cause levitation of the wafer carrier.